Security label using printed LEDs

ABSTRACT

In one embodiment, a security label comprises a random arrangement of printed LEDs. During fabrication of the label, the LEDs are energized, and the resulting dot pattern is converted into a unique digital first code and stored in a database. The label is then attached to an object to be later authenticated, or the LEDs are printed directly on the object, such as a passport, license, bank note, certificate, etc. For authenticating the object, the LEDs are energized and the dot pattern is converted into a code. The code is compared to the first code stored in the database. If there is a match, the object is authenticated. The label may also have a printed second code associated with the first code, and both codes must match codes stored in the database for authentication. The general shape of the printed pattern may convey the proper orientation of the pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on U.S. provisional application Ser. No.61/947,333, filed Mar. 3, 2014, by Mark D. Lowenthal, assigned to thepresent assignee and incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to security marks for authenticating articlesand, in particular, to a security mark containing a random array of tinyprinted light-generating devices, such as light emitting diodes (LEDs).

BACKGROUND

Many types of security marks or devices have been used to make a varietyof objects difficult to replicate or counterfeit. For example, banknotes, passports, driver licenses, and stock certificates contain avariety of security features that thwart copying, such ashard-to-replicate printed watermarks, holograms, micro-print, etc.However, all of these security features are produced using well-knowntechniques, usually printing, and the security features on each articlein the same class of articles are identical. For example, $100 bills ofthe same design generation have the same watermarks. As long as acounterfeiter can obtain sufficiently advanced equipment, it is possibleto reproduce most if not all of these security features. Any newlyintroduced security feature, such as in bank notes with the samereplicated security features, can eventually be defeated.

An optimum security feature for a wide variety of applications should beinexpensive to manufacture but should be extremely difficult to copy.Also, the security feature should be simple to authenticate. Thesecurity feature should be able to be directly printed on the article toauthenticate (e.g., for passports, licenses, bank notes, etc.) orprinted on a label or tag that is securable to an article toauthenticate (e.g., for artwork, software boxes, etc.).

SUMMARY

A printed security mark is described that contains randomly distributedlight-generating elements that are different from one security mark toanother. The security marks can be directly printed on the article to beauthenticated or be formed as a label or tag to be attached to thearticle. Since no two security marks are the same, there is no incentivefor a potential counterfeiter to use the extensive resources needed tocopy any one security mark.

In one embodiment, microscopic inorganic LEDs are printed as an ink in asmall area, such as within a 1 cm² area. Tens of LEDs, such as 20-75,are sufficient. Printing a liquid LED ink on a substrate and curing theink results in a random distribution of a range of numbers of LEDs onthe substrate. The density of LEDs in the ink determines the averagenumber of LEDs within the printed area. The LEDs are sandwiched betweentwo conductor layers, where at least one of the conductor layers istransparent, so that the LEDs are electrically connected in parallel andmay be energized by a suitable voltage. In one embodiment, the LEDs areprinted on an adhesive label smaller than a typical stamp. A metalconductor on the label may form a loop that conducts a current in anoscillating magnetic field to illuminate the LEDs so the arrangement ofLEDs can be optically detected. Alternatively, probes may supply therequired voltage to the conductor layers. Each security label may beprinted in a fraction of a second at a very low cost in a roll-to-rolltype process.

During manufacture, the LEDs in each security label are illuminated, andthe detected optical pattern is converted to a digital code and storedin a secure data base accessible via the Internet or other communicationsystem. Any additional identification of the security label or article,such as a serial number, bar code, or Quick Response Code (QR code), maybe printed on the label or article using standard black ink, and such acode is associated with the LED pattern in the database. The “lowsecurity” black ink code may simply identify a group of the labels oreach label uniquely. Since the LED layer and conductor layers can betransparent, any information printed under the LEDs/conductor layerswill be visible.

The security label is then affixed to any article to be authenticated.Alternatively, the LEDs may be printed directly on the article to beauthenticated, such as a passport.

For authenticating the article, the LEDs are illuminated, such as by aninduction power device (e.g., a coil conducting an alternating current)or probes, and the pattern of light dots is detected by an opticalcamera and converted into a unique code corresponding to the pattern.The code may correspond to the occurrence of one or more LEDs withinparticular XY cells forming a fine grid. Any conventional printed codeon the label, such as a one or two dimensional bar code, for example aQR code, may also be detected. The LED code, and optionally theconventional code, is then transmitted to a server connected to a securedatabase, such as via the Internet or a phone connection. The databasethen searches for a match of the imaged LED pattern to the storedpattern for that label and authenticates the article. This iscommunicated to the remote user via a user interface.

Since it is extremely difficult to obtain and arrange microscopic LEDsemitting a certain wavelength in a specific “random” pattern on asecurity label, the security achieved is very high. Unlike black inkcodes, the LED pattern cannot be copied with optical coping machines.

In one embodiment, blue emitting LEDs are printed. Any other color LEDsmay be printed, or multi-colored LEDs may be printed. A phosphor layeror quantum dot (QD) layer may be formed on each LED before the LEDs areprinted to wavelength-convert the LED light. If such phosphor or QDlayers are used, the positions of each LED may be detected byilluminating the security label with an externally generated blue or UVlight as a backup detection technique to lighting the LEDs themselves.

In another embodiment, microscopic particles of a phosphor or QDmaterial may be printed at a low concentration on a surface, such as fewparticles per square millimeter, using an ink, to create the randompattern. No LEDs are printed. The optical detection equipment would thenilluminate the security label with blue or UV light to cause theparticles to glow, and the detected pattern is used to authenticate thearticle.

Since every security label is unique, there is little incentive for acounterfeiter to expend the resources needed to replicate a singlesecurity label. This is especially true when combined with anauthentication database that can be queried to detect duplicate orinvalid labels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top down view of a printed security label showing a randomarray of printed LEDs and an inductive loop for powering the LEDs.

FIG. 2 is a cross-section of the security label of FIG. 1 along line 2-2in FIG. 1, showing only a few of the LEDs, whose relative sizes havebeen greatly enlarged.

FIG. 3 is an alternative cross-section of the security label of FIG. 1but with the LEDs emitting light through the transparent substrate.

FIG. 4 illustrates a detector for inductively powering the LEDs in thesecurity label of FIG. 1, optically detecting the light pattern, andcommunicating with a remote secure database for authenticating thelabel. The detector may additionally include a UV source for energizingphosphor or quantum dots.

FIG. 5 is a top down view of another embodiment of the security labelwith contact electrodes for direct probing with a current source.

FIG. 6 illustrates a detector for applying power to the LEDs in thesecurity label of FIG. 5, optically detecting the light pattern, andcommunicating with a remote secure database for authenticating thelabel. The detector may additionally include a UV source for energizingphosphor or quantum dots.

FIG. 7A is a cross-section of an LED, or other substrate, with aphosphor layer or quantum dot layer that is energized by blue or UVlight.

FIG. 7B is a top down view of a security label with a random pattern ofthe printed devices of FIG. 7A, where the printed devices areilluminated with either LED light or an external light source.

FIG. 8A illustrates a simple 5×5 grid identifying all the possible XYcells that may contain an LED, where the optically detected occurrenceor non-occurrence of an LED in each cell is used to generate a codecorresponding to the pattern of LEDs with respect to the grid. The gridlines are not actually printed but are virtual and applied duringprocessing of the LED image.

FIG. 8B illustrates an array of printed LEDs, where the LEDs have beenblocked from being printed in a certain pattern of 5 cells in the gridfor creating an additional level of security, referred to as awatermark.

FIGS. 8C-8G illustrate various mask patterns that prevent LEDs, or thedevices of FIG. 7A, from being printed in the darkened cells forcreating a watermark. When the watermark pattern of dark squares in 8Cthrough 8G are added together, they completely cover the lamp surfacewithout overlap.

FIG. 9 illustrates a virtual 10×13 grid, less than 1 square inch,superimposed over a random pattern of 65 printed microscopic LEDs, alongwith printed orientation marks used when detecting the pattern of LEDs.

FIG. 10 illustrates a random pattern of printed LEDs and a grid, wherethe printed pattern of the LEDs conveys the proper orientation whendetecting the pattern of LEDs.

FIG. 11 illustrates the LEDs of FIG. 10 without the virtual grid.

FIG. 12 illustrates another pattern of printed LEDs that identifies theproper orientation when detecting the pattern of LEDs.

FIG. 13 illustrates another pattern of printed LEDs that identifies theproper orientation when detecting the pattern of LEDs.

FIG. 14 illustrates how a coordinate system and an array of virtualcells are dynamically generated by a processing system when detectingand encoding the pattern of printed LEDs. The same processing is usedwhen storing the LED pattern in the database and later detecting the LEDpattern for authentication.

Elements that are similar or identical in the various figures arelabeled with the same numeral.

DETAILED DESCRIPTION

FIG. 1 is a top down view of a printed security label 10 showing arandom array of printed LEDs 12 and a metal inductor loop 14 forpowering the LEDs 12. The perimeter of the printed LED layer (i.e.,where the LED ink is printed) is shown by the dashed line 16. The label10 may actually represent the printed material on any substrate,including the article itself to be authenticated, such as a passport,license, etc. The label 10 may be smaller than a postage stamp (e.g.,less than 1 square inch) and have an adhesive backing. The label 10 maybe made as a sheet or roll in a high speed roll-to-roll process andsingulated. The cost per label 10 may be on the order of a penny. Thelabel 10 is very flexible.

Depending on the drive technique used and the amount of power that mustbe delivered to adequately light all the LEDs 12 in the lamp, theinductor loop 14 may be printed as a flat spiral coil of two or moreturns to form a secondary coil in order to efficiently couple with aprimary drive coil producing an oscillating magnetic field. For two ormore turns, the innermost loop connects to a first lamp electrode (e.g.,an anode) and an additional insulating layer must be printed over thecoil loops so that an electrical trace connecting the end of theoutermost winding of the spiral coil may cross over the inner loops ofthe spiral coil and make electrical contact with a second lamp electrode(e.g., a cathode) to complete the lamp-coil circuit.

FIG. 2 is a simplified cross-section of the security label 10 of FIG. 1along line 2-2 in FIG. 1, showing only a few of the LEDs 12, whoserelative sizes have been greatly enlarged for illustration.

The label 10 may be formed as follows.

In FIG. 2, a starting substrate 18 may be polycarbonate, PET(polyester), PMMA, Mylar or other type of polymer sheet, or even a thinmetal film, paper, cloth, or other material. In one embodiment, thesubstrate 18 is about 12-250 microns thick and may include a releasefilm.

A conductor layer 20 is then deposited over the substrate 18, such as byprinting. The substrate 18 and conductor layer 20 may be essentiallytransparent. For example, the conductor layer 20 may be ITO or asintered silver nano-wire mesh. If light is to be emitted in thedirection opposite to the substrate 18, the substrate 18 or conductorlayer 20 may be reflective.

A monolayer of microscopic inorganic LEDs 12 is then printed over theconductor layer 20. The LEDs 12 are vertical LEDs and include standardsemiconductor GaN layers, including an n-layer, and active layer, and ap-layer. GaN LEDs typically emit blue light. The LEDs 12, however, maybe any type of LED, based on other semiconductors and/or emitting red,green, yellow, or other color light, including light outside the visiblespectrum, such as the ultraviolet or infrared regions.

The GaN-based micro-LEDs 12 are less than a third the diameter of ahuman hair and less than a tenth as high, rendering them essentiallyinvisible to the naked eye when the LEDs 12 are spread across thesubstrate 18 to be illuminated. This attribute permits construction of anearly or partially transparent light-generating layer made withmicro-LEDs. In one embodiment, the LEDs 12 have a diameter less than 50microns and a height less than 20 microns. The number of micro-LEDdevices per unit area may be freely adjusted when applying themicro-LEDs to the substrate 18. The LEDs 12 may be printed as an inkusing screen printing or other forms of printing. Further detail offorming a light source by printing microscopic vertical LEDs, andcontrolling their orientation on a substrate, can be found in USapplication publication US 2012/0164796, entitled, Method ofManufacturing a Printable Composition of Liquid or Gel Suspension ofDiodes, assigned to the present assignee and incorporated herein byreference.

In one embodiment, an LED wafer, containing many thousands of verticalLEDs, is fabricated so that the top metal electrode 22 for each LED 12is small to allow light to exit the top surface of the LEDs 12. Thebottom metal electrode 24 is reflective (a mirror) and should have areflectivity of over 90% for visible light. Alternatively, the bottomelectrode may be made to be partially or fully transparent to allowlight to be emitted in comparable amounts both upwards away from thesubstrate and downwards through the substrate 18. With either the solidbottom reflector electrode or the transparent bottom electrode option,there is also some side light, depending on the thickness of the LED. Inthe example, the anode electrode is on top and the cathode electrode ison the bottom.

The LEDs 12 are completely formed on the wafer, including the anode andcathode metallizations, by using one or more carrier wafers during theprocessing and removing the growth substrate to gain access to both LEDsurfaces for metallization. The LED wafer is bonded to the carrier waferusing a dissolvable bonding adhesive. After the LEDs 12 are formed onthe wafer, trenches are photolithographically defined and etched in thefront surface of the wafer around each LED, to a depth equal to thebottom electrode, so that each LED 12 has a diameter of less than 50microns and a thickness of about 4-20 microns, making them essentiallyinvisible to the naked eye. A preferred shape of each LED is hexagonal.The trench etch exposes the underlying wafer bonding adhesive. Thebonding adhesive is then dissolved in a solution to release the LEDsfrom the carrier wafer. Singulation may instead be performed by thinningthe back surface of the wafer until the LEDs are singulated. The LEDs 12of FIG. 2 result, depending on the anode and cathode metallizationdesigns. The microscopic LEDs 12 are then uniformly infused in asolvent, including a viscosity-modifying polymer resin, to form an LEDink for printing, such as screen printing or flexographic printing.

The LED ink is then printed over the conductor layer 20. The orientationof the LEDs 12 can be controlled by providing a relatively tall topelectrode 22 (e.g., the anode electrode), so that the top electrode 22orients upward by taking the fluid path of least resistance through thesolvent after printing. The anode and cathode surfaces may be oppositeto those shown. The pattern of the LEDs 12 is random, but theapproximate number of LEDs 12 printed per label 10 can be controlled bythe density of LEDs 12 in the ink. The LED ink is heated (cured) toevaporate the solvent. After curing, the LEDs 12 remain attached to theunderlying conductor layer 20 with a small amount of residual resin thatwas dissolved in the LED ink as a viscosity modifier. The adhesiveproperties of the resin and the decrease in volume of resin underneaththe LEDs 12 during curing press the bottom cathode electrode 24 againstthe underlying conductor layer 20, creating a good electricalconnection. Over 90% like orientation has been achieved, althoughsatisfactory performance may be achieved with only 50% of the LEDs beingin the desired orientation for a DC driven lamp design. 50% up and 50%down is optimal for lamps that are powered with AC, such as those driventhrough inductive coupling using the conductive loop powered lamp asseen in FIG. 1.

A transparent polymer dielectric layer 26 is then selectively printedover the conductor layer 20 to encapsulate the sides of the LEDs 12 andfurther secure them in position. The ink used to form the dielectriclayer 26 pulls back from the upper surface of the LEDs 12, or de-wetsfrom the top of the LEDs 12, during curing to expose the top electrodes22. If any dielectric remains over the LEDs 12, a blanket etch step maybe performed to expose the top electrodes 22.

To produce a transparent lamp or a lamp that emits upward and away fromthe substrate 18, conductor layer 28 may be a transparent conductor suchas silver nano-wires, which is printed to contact the top electrodes 22.The conductor layer 28 is cured by lamps to create good electricalcontact to the electrodes 22.

The LEDs 12 in the monolayer, within a defined area, are connected inparallel by the conductor layers 20/28 since the LEDs 12 have the sameorientation. Since the LEDs 12 are connected in parallel, the drivingvoltage will be approximately equal to the voltage drop of a single LED12.

A flexible, transparent, polymer protective layer 30 may be printed overthe transparent conductor layer 28. Any metal pattern may then beprinted for coupling an external power source to the conductor layers20/28.

When the LEDs 12 are energized by a voltage potential across theconductor layers 20/28, very small and bright blue dots are visible. Ablue light ray 32 is shown.

For ease in energizing the LEDs 12, current through the metal inductorloop 14 is generated by inductive coupling. The inductor loop 14 may beformed by printing a metal pattern contacting the conductor layers20/28. FIG. 2 shows a cross-section of the inductor loop end portion 14Acontacting a small extension of the conductor layer 20, and anothercross-section (taken at a different location) of the inductor loop endportion 14B contacting a small extension of the conductor layer 28. Amajority of the inductor loop 14 is formed on the dielectric substrate18, and a somewhat vertical conductive trace connects the inductor loop14 to the upper end portion 14B. Each step in the vertical stair-steplike rise between the portions 14A and 14B is typically less than 10 μmand so is easily traversed by a printed trace of either an opaquereflective conductive ink or a partially or substantially transparentconductive ink. A sufficient current induced in the inductor loop 14 inthe proper direction will forward bias the LEDs 12 to illuminate them. Asuitable value resistor may also be printed between the inductor loop 14and the conductor layers 20/28 to limit current.

The bottom of the substrate 18 may be coated with an adhesive foraffixing to an article to be authenticated.

FIG. 3 is an alternative cross-sectional view of the security labelwhere the LEDs 12 emit light toward the transparent substrate 18 througha transparent conductor layer 20. A blue light ray 32 is shown. Thetransparent conductor layer 20 may be any of a variety of printabletransparent conductors or conductive ITO sputtered on the substrate 18.The protective layer 30 may optionally be a reflector, and the topconductor layer 28 may be transparent or a reflector. The layer 30 andthe surrounding exposed portions of the lamp (including portions oflayers 28, 20, 26, and possibly portions 14A, 14B and loop 14) out ontothe substrate 18 around the edges of the lamp may be coated with anadhesive, and the label 10 will then be affixed to a surface with thesubstrate 18 facing the viewer. The inductor loop 14 (including the endportions 14A and 14B) may be formed on the top surface of the substrate18 as previously shown in FIG. 2 or on the bottom of the substrate 18.

If the inductor loop 14 is formed on the lamp side of the substrate 18,they may contact the conductor layers 20/28 directly. If the inductorloop 14 is formed on the bottom surface of the substrate 18 they maycontact the conductor layers 20/28 using conductive vias 33 and 34formed through the substrate 18 to connect the inductor loop endportions 14A and 14B to the conductor layers 20/28. Similarly, in FIG.2, the inductor loop 14 may be formed on the bottom surface of thesubstrate 18, and vias may be used to contact the conductor layers20/28.

The lamp structure of FIG. 3, emitting through the substrate 18, has theadvantage that, if the label is affixed to a surface with an adhesiveapplied on top of the protective layer 30, an appropriate adhesive maybe selected that will tear the lamp apart if an attempt is made toremove the label from the surface it has been affixed to.

The label 10 is very flexible and has a thickness on the order of paperor cloth, such as between 5-13 mils.

The labels 10 may be formed using a roll-to-roll process where the LEDs12 and other layers are continuously printed on a single substrate 18and then singulated. One surface of the labels may have a tacky adhesiveapplied to them, and the labels may then be applied to a wax film forcreating inexpensive rolls of many labels 10. Since the positions ofLEDs 12 for each label 10 are random when printed, the pattern of LEDsin each label 10 will be different and unique.

In addition to printing the LEDs 12, a black ink code, such as a machinereadable serial number, bar code, or QR code may optionally also beprinted on a non-light emitting portion surface of the label 10 toprovide a secondary degree of security. The substrate 18, LED layer, andconductor layers are substantially transparent so the black ink code mayeven be printed below the LED layer. This black ink code may identifythe batch of labels 10 or may uniquely identify the label 10. The blackink code may even be printed directly on the article to be authenticatedrather on the label 10. The latter option allows the user of the labelto define the association of a given black in code on the article beingsecurely identified with the label 10 placed on that article. Theproducer of the label 10 will then be guaranteed to have no knowledge ofvalid pairings of black ink security codes and secure LED labels 10 inorder to produce an enhanced level of security. Instead of using blackink, any other color ink may be used. The ink may even be magnetic, oran invisible fluorescent ink, or a color changing ink.

During the roll-to-roll manufacturing of the labels 10, the LEDs 12 ineach label 10 are energized by an inductive coil, and an optical imager(a camera), synchronized with the energization, takes a picture of thedot pattern (e.g., blue dots) and generates a digital code based on thedot pattern. For example, the processing system in the detector maydivide the picture into a grid of small cells (e.g., 10×10 cells) andgenerate a code that reflects which cells contain one or more dots. Thedot code may also be associated with the machine-readable black ink codeon the label 10. The dot code and black ink code for each label 10 arethen stored in a secure database that is accessible via the Internet orother communication system.

The labels 10 are then applied by the user to the articles to beauthenticated. Alternatively, the various layers may be directly printedon the articles, such as bank notes, certificates, passports,prescription drug labels, licenses, credit cards, debit cards, etc.

When someone desires to later authenticate the article, the followingdevices and methods may be used.

FIG. 4 illustrates one embodiment of a detector 38 that powers the LEDs12 and authenticates the label 10.

The label 10, or article having the printed layers, is positioned infront of a digital imager 40, such as a camera. The imager 40 may behand held. The same type of detector 38 may also be used duringmanufacturing of the label 10 to store the unique code conveyed by thedot pattern. FIG. 4 shows the label 10 supported on a surface 42, whichmay be the article to be authenticated. The field of view of the imager40 is shown by the dashed lines 44.

A metal coil 46 (the primary coil) centered over the label 10 is thenenergized by one or more pulses from a power supply 48 to create anelectromagnetic field. An AC signal may also be applied to the coil 46.The electromagnetic field induces a current through the inductor loop 14on the label and forward biases the LEDs 12 to continuously or brieflyilluminate them.

Power may be transferred using either an RF field produced by continuousAC power to the coil 46 or pulsed, using a flyback drive approach.Driving the coil 46 with continuous AC, with a frequency from 10 kHz to100's of kHz, will light LEDs of both orientations, with one populationof LEDs lit during each half of the AC cycle, and a blue dot patternwill coincide with the locations of every printed LED 12. Alternatively,low duty-cycle square wave pulses, with a frequency from 10 KHz to 100'sof kHz, may be used to induce a current in the inductor loop 14 with avoltage high enough to light LEDs of one orientation each time thecurrent is supplied to the coil 46. If the inductor loop 14 is printedsuch that it has a high enough series resistance, the induced voltagesignal then damps out to below the micro-LED turn-on voltage of the LEDsas the voltage in the coil 46 and loop 14 swings to the reversepolarity. This permits the LED driver to selectively light only the“down” or the “up” LEDs so that the digital imager 40 may take anexposure of the lit label 10 that spans multiple driver cycles. Thepolarity of the pulses in the coil 46 is used to select whether the “up”or “down” LEDs 12 are to be lit. The combined pattern of up and downLEDs may be part of the unique code.

Further details of a technique to energize LEDs using an inductor coiland a driver may be found in U.S. Pat. No. 8,413,359, assigned to thepresent assignee and incorporated herein by reference.

The LED wafer, prior to singulation to form the microscopic LEDs 12 forprinting, may be coated with a phosphor layer or quantum dot (QD) layerover their emitting surfaces during fabrication. Various semiconductorlithographic techniques may be used to prevent the phosphor layer orquantum dot layer from coating the top electrode. The phosphor or QDsare energized by the blue LED light or an external blue or UV source todisplay a random arrangement of lit dots in the label 10. The phosphoror QD layer may emit any color light, such as blue, red, green, yellow,or white. Some of the LED light may leak through the phosphor or QDlayer to combine with the phosphor light. In the event that a powersource is not available to energize the LEDs 12 during authentication,or if there is a circuit failure, the detector 38 includes UV lightemitters 50 that illuminate the surface of the label 10. The phosphor orQD lit dots are then detected by the imager 40 to perform theauthentication.

Once the random arrangement of dots is illuminated, either by the LEDs12 or the external light source, a programmed processor/memory system 51connected to the imager 40 records the image and generates the uniquecode for the dot pattern in the same manner as the code was generatedduring the manufacture of the label 10. Any other identifying mark onthe label 10, such as a serial number, is also optically detected andassociated with the dot code. A printed serial number on the articleitself, such as a passport, banknote, license, or certificate, may alsobe optically detected by the imager 40 and ultimately cross-referencedwith the dot code.

The dot code and other optically detected information are thentransmitted via a communications network 52 to a secure database 54. Theuser uses a user interface 56 to control the authentication process andreceive the authentication information. The user interface 56 may be asimple button pad with a display.

The database 54 then compares the dot code to a stored dot code and, ifthere is a match, the label 10 is deemed authentic, along with theassociated article. The optically detected label serial number (or otherprinted code) may also be detected, and both codes are compared withassociated codes in the database 54 for additional security. Theidentification that the label 10 is authentic may be transmitted to adisplay in the user interface 56, or other systems may be used toregister that the label 10 is authentic or not authentic.

FIG. 5 illustrates another embodiment of a label 60 formed in the sameway as the label 10 except there is no inductor loop. Instead, theconductor layers 20/28 are terminated with metal pads 62 and 64 forbeing contacted by probes in the detector. A sufficient voltage appliedto the pads 62/64 will illuminate the LEDs 12.

FIG. 6 illustrates a detector 68 for authenticating the label 60. Allelements are the same as the detector 38 of FIG. 4 except for metalprobes 70, for applying a voltage to the pads 62/64, and a polarityswitchable DC voltage source 72, which can be used to selectivelyilluminate LEDs 12 in each orientation. A simple AC voltage source maybe used to illuminate both orientations of LEDs 12 without orientationselectability.

The LEDs 12 and conductors/pads may be printed so that the probes canenergize selected sections of the label 60. A single common (e.g.,grounded) probe may be used, and the various LED sections may beilluminated by one or more positive or negative voltage probes. A metalpad for a section may be printed along an associated side of the label60.

In another embodiment, a magnified image of the LEDs 12 may be viewedwithout even energizing the LEDs to detect the LED pattern. The patterncode may then be compared to the stored code for authentication.

In another embodiment, as shown in FIG. 7A, the light-generating devicesdo not use LEDs. FIG. 7A shows that any substrate 76, such as silicon, aceramic, a polymer, etc., can have a phosphor or QD layer 78 depositedover it prior to singulation, and the microscopic singulated devices 80are then printed on a flexible substrate 82 (FIG. 7B) as an ink to forma security label 84. The shapes of the devices cause the devices toself-orient during printing. An external UV or blue light sourceenergizes the devices 80 instead of using LEDs. No voltage source orconductor layers are needed.

Alternatively, substantially uniform particles of phosphor or quantumdots are printed to form a random array of the microscopic particles ona label, and a UV or blue light source energizes the particles insteadof using LEDs. The phosphor or quantum dot particles may be directlydispersed in an ink at a low concentration so that no substrate 76 (FIG.7A) is needed. The ink solvent is evaporated, leaving thewavelength-conversion particles randomly scattered on the label surface.No voltage source or conductor layers are needed.

In the sample label 84 of FIG. 7B, there are no active devices, and thewavelength-conversion particles, such as the devices 80 or particles,are randomly arranged on the substrate 82. The arrangement of dots, whenilluminated, serves the same function as the LEDs 12 of FIGS. 1 and 5.However, the security is lowered since there is no need to form therelatively complex LEDs 12.

Each label, using any of the above described techniques, may containseveral dozen micro-LEDs 12 and may be under a square inch in area, forexample, as small as 1/64 of a square inch to several square inches inarea. The label is affixed to the surface of some article whoseauthenticity must be verified at a later time. The printed micro-LEDlamp labels may be transferred to a target surface using any number ofwell-known techniques used by industry to transfer labels and apply themto surfaces. For example, the micro-LED lamp security labels may beprinted on a continuous or semi-continuous tape to produce a series oflamps along the tape length. The tape may be backed with adhesives andcut to separate the lamps or separated along perforations between thelamps on the tape, or individual lamps on their substrate with adhesivebacking may be affixed to a continuous release tape after being cut fromthe original micro-LED press sheet. The adhesive may be pressuresensitive, heat sensitive, light-activated, or may use some otheradhesion activating technique appropriate for the surface to which thelabel is to be laminated. Alternatively, the substrate or the topprotective coating of the lamp itself may be made completely of a lowglass transition temperature polymer that can be affixed permanently toa preferably absorbent surface using a heat lamination process thatmerges the lamp and the target surface.

The adhesive-lamp combination may be constructed in such a manner thatremoving the tape will destroy the lamp, making it impossible torecreate the original dot pattern. For example, each lamp may beover-coated with a strong contact adhesive, which has greater cohesionwith the target object's surface than the interlayer cohesion between atleast two active layers within the lamp. Attempting to remove the labelfrom the object to which it has been affixed will split the lamp betweenactive layers, permanently destroying all or some portion of the lamp'slightability.

The labels may also be used to secure containers, where the label isaffixed as a seal and must be broken or removed to open the container. Abroken label will not light and cannot be repaired. Such a seal may beused for software cases, CD cases, DVD cases, etc. Each unique micro-LEDsecurity label lamp in itself is difficult to produce, greater than thedifficulty of reproducing a hologram label.

Instead of a label with an adhesive, the lamp may be a non-adhesive tagthat is secured to the object to be authenticated.

To add an additional layer of security, a hidden “watermark” may beintegrated into the micro-LED lamp. Watermarks can be easily created byincluding a “no-go” area within the printed lamp, where the randomlyscattered micro-LEDs 12 will never be printed. A different hiddenwatermark or set of watermarks may be used for each object class to besecurely identified. If the shape of the watermark is designed properly,composed of narrow sinuous lines and/or dots or squares, it will not bevisibly detectable against the random background of lit micro-LEDs. Anymicro-LED label that is lit, imaged, and compared to the secret no-gomap for that label type will immediately be detected as a forgery if amicro-LED appears in a no-go watermark area.

FIGS. 8A-8G are used to describe possible simple watermarks. FIG. 8Aillustrates a 5×5 grid of cells 86, where any combination of the cellsmay be blocked using a printed hydro-phobic mask or the LED ink isprevented from being printed in the selected cells by a screen printingmask. The grid lines are not printed and represent cell locationsprogrammed into a processor. An optically detectable “proper-orientationmark” 87 is printed on the label. FIG. 8B illustrates a printed labelcontaining LEDs 12, where the LEDs 12 are prevented from being printedin certain no-go cells. FIGS. 8C-8G illustrate a few of the possiblecombinations of no-go areas 88 in black, where five of the cells areno-go cells. The locations of the LEDs 12 in FIG. 8B coincide with thewatermark of FIG. 8D. With a higher concentration of printed LEDs 12, atleast one LED would be printed in the allowable cells.

In actuality, the grid size will be larger than 5×5, and there will bemany more combinations of no-go cells. The pattern of LEDs 12 may not bein a grid pattern at all, but instead be arranged as a complete tilingof the lamp surface with non-overlapping irregular shapes.

Even with only 10% to 20% of the secure lamp surface dedicated to thewatermark, a virtually infinite number of distinct watermarks arepossible. This opens the possibility of using more than one watermarkdesign, say four or five, for a given class of objects to be validated.If several different watermarks are used, determining any one watermarkis difficult. However, it may still be possible to create a composite ofall the known watermarks by examining a large number of labels and thencreating forgeries based on this synthesized watermark. To avoid this,the watermarks used to identify a particular class of objects may beselected to use mutually exclusive areas of the lamp such that the setof watermarks when combined together perfectly and without overlap tilethe surface of the lamp, making it impossible to make any one of thewatermarks in the set of watermarks visible by summing together asampling of many lamps. The watermarks shown in FIG. 8C through FIG. 8Gform such a set of watermarks, in which the entire lamp surface is tiledwithout overlap when all five of the watermark patterns are overlain ontop of one another.

The 5×5 grid example has a fairly small number of watermark and IDpossibilities and is only used as an example. In an actualimplementation using a sampling grid, the sampling grid would be greaterthan 10×10, or preferably even larger, say 10×15. For a 10×15 grid (150cells) containing 5 watermarks, with each watermark including 30 cells,there are a total of 3.220×10³¹ possible watermark combinations.

The number of possible watermarks in such a lamp permits watermarks setsto be designed and assigned freely, with no concern that duplicatewatermark sets will accidentally be assigned to two different classes ofobjects needing different ID tags. To increase the computationalcomplexity of trying to break the watermark security further yet, thenumber of cells in each watermark in the watermark set may differsomewhat, but the watermarks will still sum to tile the entire lampsampling grid.

The entire set of valid watermarks that authenticate a given article arestored in a secure database. There is no reason to test any LEDs afterprinting for storage of the illuminated dot pattern in the database,since it is assumed the LED patterns coincide with stored watermarks.Any counterfeit label has an extremely small chance of matching a storedwatermark. For authentication of any label containing a watermark, theLEDs are energized by the detector of FIG. 4 or 6, and the resulting“dark cell” pattern is compared to the set of stored watermarks todetermine if there is a match. If so, the user is informed that thelabel is authentic. Both the watermark and the dot code authenticationtechniques may be used in combination if a two level authenticationsystem is desired, one level using the watermark that permits anonymousvalidation without tracking, and the other using the dot code that canbe used to identify a specific label previously recorded in a database.

As an example of the use of a watermark to authenticate an article,let's assume the company Gucci America, Inc. wants to implement a meansof authenticating that 1000 Gucci handbags of a certain style areauthentic. A tag, implementing the present invention, can be secured toeach of the handbags at the manufacturing facility. When the tag isoptically detected at a point of sale, it is authenticated by theinventive system, proving that the handbag is authentic. In one exampleto make the tag, the tag has printed on it microscopic LEDs over avirtual grid of cells, where the LEDs are blocked from being printed incertain predetermined cells so as to form a watermark. There may be manymillions of watermark possibilities, but only five different watermarkswill be assigned to the 1000 handbags, such as the five watermarks ofFIGS. 8C-8G, although the grid size will be much larger (e.g., 100×100cells) than the 5×5 grid size of FIGS. 8C-8G. Since there are 1000handbags and five different tags, groups of 200 handbags will have thesame tag. Multiple watermarks are assigned to the 1000 handbags so thata forger cannot reverse engineer a single watermark by superimposing theLED patterns of a large number of tags. Ideally, the superimposedcombination of the five watermarks in the set assigned to the 1000hangbags completely fills in all cells in the grid without any gap oroverlap so there is no clue to the watermarks obtained by superimposingthe LED patterns on the tags. Since the locations of the individualprinted LEDs are random due to the printing process, and the LEDdistribution is relatively sparse, the locations of the cell boundariesare hidden from a forger. Digital codes corresponding to the fivewatermarks associated with the 1000 handbags are stored in a securedatabase. For authentication of a handbag, the attached tag is opticallydetected at the point of sale to create a digital code corresponding tothe LED pattern. The code corresponding to the LED pattern also conveysthe watermark since it indirectly conveys the pattern of cells that donot contain any LEDs. The code is transmitted to the database andprocessed to determine the watermark pattern (the pattern of no cellscontaining any LEDs). If the watermark pattern matches a storedwatermark pattern for that style of handbag, the handbag is deemedauthentic. The processing for determining the watermark on the tag mayalso be performed by the detector at the point of sale. The specificlocations of the printed LEDs within the various cells are not relevantfor authentication since only the watermark (absence of LEDs in cells)is used. Since the specific locations of each of the LEDs are notrelevant, the optical detection of the watermark may be simplified bysimply determining which cells do not contain any LEDs and codifyingsuch information. In such a case, the detector software effectivelyoverlays a virtual grid pattern on the detection area and examines eachcell to determine whether there are any LEDs in the cell.

For another style of Gucci handbag, a different set of five differentwatermarks may be assigned to that style. Such watermarks will beassociated with that style and stored in the database. Forauthentication, both the style handbag and watermark pattern aretransmitted to the database for matching to a stored style/watermark.The particular style of handbag may be conveyed to the database by aseparate code on the tag, such as a machine-readable bar code or stylenumber.

In the example, there are five watermarks assigned to a particular typeof article, but there may be any other number of watermarks in the set,such as 3, 4, 10, etc.

In another embodiment, instead of printing light-generating devices toform the watermark pattern, such as LEDs, phosphor particles, or quantumdots, non-light-generating particles can be used, such as a blackparticles (e.g., carbon) suspended in a solvent as a printable ink thencured to evaporate the solvent. The locations of the black (or othercolor) particles (dots) on the authentication tool (e.g., label) wouldbe random, but the particles would be masked from being printed in thepredetermined exclusion cells to form the watermark. The random printingof the particles, and the dispersion of the particles, would not conveyany grid cell boundaries to a potential forger of the watermark. Thelight source for illuminating the authentication tool can be ambientlight or a suitable light source on the detector. By using small blackparticles, the authentication tool can use a very high resolution cellgrid, hidden in an area that appears to the eye to simply be a randomdot screening pattern to produce a tint on a particular area of artwork.Only a portion of the area tinted with the particles might actuallycontain the watermark. The rest of the area could simply be a random dot(particle) pattern to further disguise the tinted area of the artworkcontaining the random dot (particle) pattern used to form the watermark.The authentication tool may thus appear semi-transparent, such as anoverall gray color.

In order to maintain the maximum security of the watermark being used,the manufacturing site where the labels are printed should be kept underhigh security to prevent unauthorized access to information about thewatermark set being used for any given class of objects to be secured.The press sheets containing the lamps must be diced into lamps and theirorder should be randomized before allowing them to exit the securedfacility. It might be possible to decrypt the entire watermark set bylooking only at printed samples if the original position of each labelon the press-sheet were known and a sufficiently large number of suchlabels could be analyzed. Once randomized, the only concern would betheft of a shipment of secure labels. Watermark sets could be changedfairly frequently so that blocks of labels of which some had been stolencould be subjected to more intense scrutiny for validity, or simplydestroyed and never used if the theft is detected before the objects towhich the security labels are affixed have been shipped. In fact, eachshipment could use a different watermark set, since the universe ofpossible watermarks is very large (10 ³¹ in the moderately large exampleabove). If the entire shipment was delivered without any theft detected,then all the watermarked labels in the shipment could be safely used inthe desired application.

To guard against the use of a watermark set stolen from the securemicro-LED label manufacturing site, the secure labels may be used inpairs. Dozens of valid watermark sets could be defined, creating alibrary of watermark sets, but only specific combinations of pairs ofwatermark sets would be considered valid. These pairings could beselected and stored securely at the label consumption entity, unknown topersonnel at the secure label manufacturing site. Stealing any or allwatermark sets would be of no use without knowing how to validly pairthem, thus enhancing security of the lamp labels, independent ofsecurity measures at the lamp label manufacturing facility.

Additionally, the queries sent to the secure watermark database could belogged and stored for some period of time. If a flood of identicalqueries are detected from a variety of sites scanning the securitylabels, this can be used as an indication that someone has managed toexactly reproduce a single or a small number of micro-LED securitylabels, since each watermark should be unique in order to pass thewatermark security test. Once detected, this would give an opportunityto investigate such incidents, if they occurred. Note that very closematches might also be detectable in order to prevent attacks thatinvolve producing forgeries that simply subtract a few micro-LEDs from aknown valid micro-LED security label.

Many objects that are popular with counterfeiters are possibleapplications for the type of secure label described above. Currency isof course an excellent example. The advantage of the above system isthat it does not rely on a permanently recorded and tracked optical IDunique to each printed to bill, and so avoids civil liberties concernsthat might arise from the possibility of tracking money everywhere it isused. Other possible examples are, but not limited to, software,expensive designer apparel/accessories, and prescription drugs labels.

As previously mentioned, the random locations of the printed microscopicLEDs (or other microscopic light-generating devices) within a virtualpartitioning of the lamp surface, such as a grid, are used to generate aunique digital code of 1s and 0s, where the presence of one or more LEDsin a cell is a 1 bit, and the absence of any LEDs in a cell is a 0 bit.For example, in a non-watermark case, a 10×10 grid will provide a 100position digital code, having 1.267×10³⁰ possible codes. The density ofthe LEDs in the ink will determine an average number of cells thatcontain an LED. The density of LEDs in the ink can be changed from lotto lot to maximize the range of codes. The digital code is read duringfabrication when the LEDs are illuminated, and the code is stored in adatabase as a series of 1s and 0s. During authentication of the label,the LEDs are energized and optically detected. The dots in the image areelectronically compared to a virtual XY grid to derive the correspondingdigital code of 1s and 0s. This code is then transmitted to the databaseto determine whether the code exists in the database. If so, it isassumed the label or tag is authentic.

The micro-LED security label or tape may be used as a guaranteed uniqueID tag. The locations of all the micro-LEDs in a lamp form a completelyunique identifier, akin to a serial number, but more similar to therandomly generated Global Unit IDentifier (GUID) codes commonly used inmany computer applications where a world-wide, all-time, guaranteedunique identifier is needed. GUID code numbers are so large, typicallycomposed of 122 random bits, that even if billions and billions of newGUID code are generated randomly the chances of any two being alike is avery close approximation to zero.

As an example, a cell array of 10 rows and 13 columns has 130 cells 86and is shown in FIG. 9, giving a 130-bit number. Printed orientationmarks 87 and 90 are shown. If the printed density of micro-LEDs 12 isadjusted to produce approximately 65 micro-LEDs, then approximately2¹³⁰/2⁶⁵=˜2⁶⁵ possible combinations are possible, or about 3.689×10¹⁹.Therefore, although the codes are randomly generated and theoreticallymay repeat, the chances of a repetition are unlikely. This example isonly an approximation, since lamps will have a distribution of total LEDcounts centered on 65 LEDs, with some lamps having as few as 45 andothers as many as 85 micro-LEDs. This has the effect of actuallyincreasing the number of possible unique combinations significantly.Additionally, some sampling cells 86 will contain more than onemicro-LED. Using this scheme, the possible-combinations as a function ofaverage number of LEDs divided by the number of sampling cells reaches amaximum at 0.5. Thus, the optimum number of LEDs to print on such aunique ID tag is approximately equal to half the number of grid cellssampled on the tag.

An even larger number of possible unique tags may be created by takinginto account not only the micro-LED positions, but the up or downorientation of each micro-LED in the micro-LED lamp label.

Instead of LEDs, phosphor particles (or microscopic substrates coatedwith a phosphor layer) may be printed and energized with blue or UVlight. The phosphor particles may emit yellow light or any other color.Quantum dots may also be printed.

Any version of the unique micro-LED lamp label/tag identifier describedabove or elsewhere in this document may be affixed to an object forwhich a unique identifier is desired. Each micro-LED lamp isfingerprinted either when the micro-LED lamp is initially printed orafter it has been affixed to the object to be securely tagged, byimaging the micro-LED lamp while it is lit and recording the image. IfUV tagged micro-LEDs are used, the UV illuminated image of the patternof all the micro-LEDs in the printed security lamp may also be recorded.The lit-LED image, and optionally the UV illuminated image, are encodedappropriately into a compact digital format. This lamp fingerprint datais then stored in a secure database with the fingerprint data indexedfor searchability. The secure database may then only be blindly queriedfor “Valid” or “Invalid” responses. At a later time and/or distantlocation, the energized lamp may be imaged and its encoded image used toquery the secure lamp fingerprint database in order to verify theauthenticity of the object to which the security lamp is affixed. Themicro-LED secure label may be tracked by recording the location eachtime it is scanned.

Any system used to definitively locate LEDs on a lamp in such a way thatthe LED locations can be matched to a fingerprint stored in a databaserequires a method of establishing a fixed coordinate system by which theLED positions may be accurately and repeatably measured by an imagingdevice. Three problems must be addressed: measuring the micro-LED lampcoordinate X and Y axis rotation, determining the coordinate systemorigin position, and determining the correct coordinate system scalingalong the X and Y axes.

When a lamp is being imaged, the imager needs to allow for the fact thatthe tag (or label) will be in an unknown orientation. It may be rotatedaround an axis in line with the imaging system, or worse yet, the planeof the tag may not be perpendicular to the imaging axis. If themicro-LED tag lamp has a simple rectangular or square shape, or evenworse, round, it could have several or many possible orientations evenwhen its plane is perpendicular to the viewing axis. To determine thelamp's orientation, a lamp may be accompanied by two printed solid linesof well-defined standard length next to two adjacent lamp edges andpossibly intersecting at the coordinate system origin, such as theprinted mark 87 in FIG. 9. For greater reliability, an additional pairof short lines, such as the orientation mark 90, may be printed at thelamp corner opposite the origin corner established by the longer lines(mark 87). These marks may be printed as solid ink lines of black oranother graphically appropriate visible color. Alternatively, the linesmay also be printed using invisible ink made visible only whenilluminated with the proper range of wavelengths, UV light being anexample. In this case, the micro-LED security lamp validation imager,examples of which can be seen in FIGS. 4 and 6, would require anintegrated UV illuminator in order to properly image the coordinatesystem markings. Other orientation feature shapes are also possible.

The markings described above solve all three problems: the intersectionof the two long lines (mark 87) establish a coordinate origin, theposition of the lines themselves can be used to determine theorientation of the X and Y axis, and the length of the lines can be usedto determine the scale of the coordinate system. The optional additionalpair of short lines (mark 90) can be used to detect distortions in thesurface and as a redundant check on the scale of the coordinate system.This system is highly robust, correctly determining the micro-LED lampposition in any possible orientation in 3D space, as long as the face ofthe lamp is visible to the imager.

One drawback of the orientation system based on printed lines of inkadjacent to the lamp is that imaging both the lines and the brightly litLEDs simultaneously may be difficult because of the differing exposurelevels needed to accurately image both. Two images with differentexposures may be taken, but might be difficult to correlate with oneanother if the tag being illuminated is moving continuously duringimaging. Short exposures with as short a time as possible betweenexposures is required to handle capturing and validating a movingsecurity tag.

FIGS. 10-14 illustrate an alternate method of establishing a coordinatesystem using the shape formed by the micro-LEDs in the lamp itself toorient the lamp properly for fingerprinting and authenticityverification, thus avoiding the need for an additional printedorientation mark. The lamp may be shaped like a keystone, an isoscelestriangle or trapezoid, a capital-T, or any number of asymmetric shapesthat have only one possible orientation through 360 degrees of rotation.

FIG. 10 illustrates a rectangle shape with one extended row and columnof LEDs 12 to create orientation guides 96 and 97. The grid lines arenot printed but are programmed into a processor system to identify thecells in the array in which are located one or more LEDs 12. FIG. 11shows the printed LEDs 12 of FIG. 10 without the grid lines. Thecombination of cells containing either zero or at least one LED 12corresponds to a digital code, such as a code where each cell is a 1 or0 bit and the combination of bits forms a unique string of bits. Aspreviously mentioned, the unique code is stored in a database, andauthenticating the tag or label involves optically sensing the locationsof the illuminated dots, deriving the code, and comparing the derivedcode with the stored code. In the examples of FIGS. 10-14 the density ofLEDs 12 in the ink randomly prints between about 65-75 LEDs over thelabel area.

FIG. 12 illustrates an isosceles triangular arrangement of LEDs 12 overa virtual grid, and FIG. 13 illustrates a right triangle arrangement ofLEDs 12. No separate orientation marks are required, since theasymmetrical shape of the LED pattern identifies the correct orientationfor generating the code.

Although the micro-LEDs are very robust, to be insensitive toelectrically or mechanically damaged LEDs that no longer light, suchorientation schemes, especially the one shown in FIG. 10, would requiremicro-LEDs that are visible when illuminated with UV, an optionpreviously described above where the LEDs contain a phosphor or quantumdot layer. The edges and corners of the smallest trapezoid that cancompletely enclose all the micro-LEDs in the lamp (when illuminatedunder UV) are then used to establish the coordinate system used tomeasure the micro-LED positions, as shown in FIG. 14. FIG. 14illustrates the generally triangular LED pattern of FIG. 13 without thegrid lines. As long as the detection is consistent between initiallydetecting the LEDs for storing the code and later authenticating thecode, the proper codes will be compared. In FIG. 14, the edge-most LEDsare detected to create the trapezoidal outline 100 of the LED pattern.The actual area for printing the LEDs 12 is shown by the dashed outline102. The grid array, having predetermined size cells, is then createdbased on the bottom edge of the trapezoid and the left edge of thetrapezoid. Note that the Y axis 103 is skewed with respect to theprinting area edge and not perpendicular to the X axis. The 0,0coordinate position 104 is shown. The cell divisions 106 are shown alongthe X and Y axes to form an array of approximately 150 cells. Using thistechnique of electronically orientating the LED pattern, there is noneed for the user to orient the label in any way when the LED pattern isdetected during authentication. All the orienting, for both initiallygenerating the code and for authentication, is performed automaticallyusing programmed processors.

The technique of classifying a cell as a 1 or 0 depending if there areone or more LEDs within a cell boundary is referred to herein as abinning technique. The micro-LED cell binning technique would have tohandle LEDs that are very close to binning cell partition lines betweenbinning sampling cells. These could be sampled as a separate populationfrom the micro-LEDs that are well within a sampling cell. Two keys couldbe produced from these two populations. A first low error rate key,constructed from micro-LEDs far away from binning cell partition lines,could be used as the primary key into the secure database. The remainingmicro-LEDs near grid-binning lines could then be used to form a second,higher error rate key, which could be used to search the result setreturned by the primary key search.

As previously mentioned, for a damaged lamp, micro-LEDs in the lamphaving a phosphor layer can be imaged by illuminating the tag with UVlight, rather than applying electrical power. This can also provideenough information to fully fingerprint a lamp. In fact, without usingmicro-LEDs, a unique optical ID tag may be created using onlyfluorescent particles and applying all the techniques for encoding afingerprint for each ID, watermark, etc. as described above. However,printing micro-particles containing fluorescent materials is fairlystraightforward, and can be fairly easily replicated using inkjetprinting techniques. The additional complexity of both obtaining andprinting functioning micro-LEDs vastly increases the difficulty ofproducing forgeries and the pattern of up and down orientation of themicro-LEDs in the lamp eliminates inkjet systems as a forging techniqueentirely.

One possible example of combining all the techniques described abovetogether follows. Other methods of combining the UV-illuminatedmicro-LED location data, lit micro-LED location data, and LED up/downdata are of course possible. The fingerprint extracted from the lamp mayconsist of a tiered set of binary keys. Given N grid binning cells, eachbit of each key represents one cell. In this example, six keys areextracted from the lamp:

-   -   1) Illuminated only with UV light:        -   a. N-bit key, 1s=cell contains a micro-LED far away from a            binning boundary, otherwise 0. (No differentiation made            between up and down orientation LEDs.)    -   b. N-bit key, 1s=cell contains a micro-LED near or on a binning        boundary, otherwise 0. (No differentiation made between up and        down orientation LEDs.)    -   2) Micro-LEDs lit with power applied:        -   a. Lit “up” micro-LEDs:            -   i. N-bit key, 1s=cell contains “up” micro-LED far away                from a binning boundary, otherwise 0.            -   ii. N-bit key, 1s=cell contains “up” micro-LED near or                on a binning boundary, otherwise 0.        -   b. Lit “down” micro-LEDs:            -   i. N-bit key, 1s=cell contains “down” micro-LED far away                from a binning boundary, otherwise 0.            -   ii. N-bit key, 1s=cell contains “down” micro-LED near or                on a binning boundary, otherwise 0.

Note that up and down micro-LEDs may both be present in the same binningcell, and some LEDs may not be electrically lightable, but will bevisible with UV illumination.

The 1a keys may be used for initial indexing into the fingerprintdatabase, followed by an examination of the 2a-i and 2b-i key values. Ifa match is found, the degree of match of the 2a-ii and 2b-ii values canbe used to decide whether the Unique ID tag will be considered avalidated match to the secure database store. Note that these keys canbe extracted from the micro-LED lamp and sent blindly as a series ofonly a few hundred bits to the secure server to return a “good” or“invalid” result.

Rather than binning LED positions into a sampling grid in the labelreader and its integrated processor, the raw LED coordinates on theimaged lamp surface or even the image of the lit lamp may be sent to thesecure server, where LED binning and subsequent database lookup andwatermark detection are performed. This has the advantage of hiding thespecific algorithms used by keeping them protected in the securedatabase facility. Examination of the software and firmware within thelamp reader in the field will provide a forger no clues as to how toproceed in producing counterfeits of the secure lamps.

Alternatively, rather than binning each micro-LED position,neural-network/database techniques might be used to fingerprint eachlamp and store its fingerprint in the secure database. Other schemesbased on each micro-LED position rather than binning may also be used tocreate a binary fingerprint of the lamp.

A variety of concepts can be applied to any of the security lampsdescribed in this disclosure. Some examples, which are described below,may not be appropriate for the highest security designs using compoundwatermark and unique optical IDs described above.

-   -   The shape of the security lamp might have a distinctive shape,        such as a logo, in order to render the security lamp distinctive        from security lamps used by other companies. Such a lamp may        still including a hidden watermark set.    -   The hidden watermark itself might be a logo to render the        security lamp distinctive from security lamps used by other        companies.    -   The lamp may be transparent (i.e., substrate and conductor        layers are transparent) so that it may be applied over all or        some portion of a photograph on an ID card or other document,        such as a passport. Depositing a transparent lamp over the        photograph in an ID would make it difficult or impossible to        replace the photograph with a false one.    -   The dielectric of the lamp may be selected such that it has a        controlled, recoverable breakdown behavior at fairly low        voltages (less than 10V) to protect the micro-LEDs from        accidental or intentional overvoltage.    -   A zener diode, either printed or placed using well know        semiconductor industry techniques such as pick-and-place, may be        connected in parallel with the lamp in order to protect the        micro-LEDS from accidental or intentional overvoltage.

All features described herein may be combined in various combinations toachieve a desired function.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects and, therefore, the appended claims areto encompass within their scope all such changes and modifications asfall within the true spirit and scope of this invention.

What is claimed is:
 1. An authentication system comprising: randomlyprinted light-generating devices on a substrate, wherein thelight-generating devices comprise light emitting diodes (LEDs), whereinthe LEDs are connected in parallel such that all the LEDs on thesubstrate are illuminated at the same time, the randomly printed LEDs onthe substrate being an authentication tool; an energization system,external to the substrate, configured for providing power to the LEDs tocause all LEDs on the substrate to be illuminated at the same time,wherein the illuminated LEDs create a static light pattern; an opticaldetector configured for detecting the static light pattern from the LEDsin the authentication tool after the LEDs have been illuminated; aprocessing system coupled to the detector and configured to generate afirst code corresponding to the static light pattern; a communicationsystem coupled to transmit the first code to a database storingpre-stored codes; and an interface system configured to convey that thefirst code matched one of the pre-stored codes, signifying that theauthentication tool is authentic.
 2. The system of claim 1 wherein thelight-generating devices are coupled to receive an energizing voltagesupplied by the energizing system.
 3. The system of claim 2 wherein thelight-generating devices further include a wavelength-conversionmaterial that emits a wavelength different from an energizingwavelength.
 4. The system of claim 1 wherein the light-generatingdevices comprise a wavelength-conversion material that emits awavelength different from an energizing wavelength, wherein theenergizing system emits the energizing wavelength.
 5. The system ofclaim 1 wherein the light-generating devices comprise microscopic lightemitting diodes (LEDs) that have been printed over the substrate as anink, wherein the ink is then cured.
 6. The system of claim 5 wherein theauthentication tool further comprises two conductor layers connectingthe LEDs in parallel, wherein at least one of the conductor layersallows light to pass through.
 7. The system of claim 1 wherein theauthentication tool is an adhesive label.
 8. The system of claim 1wherein the authentication tool is a tag configured to be attached to anobject to be authenticated.
 9. The system of claim 1 wherein thelight-generating devices are printed on an object to be authenticated.10. The system of claim 1 wherein the substrate comprises an object tobe authenticated.
 11. The system of claim 1 wherein the light-generatingdevices comprise light emitting diodes (LEDs) coupled to an inductorloop, wherein the energizing system generates a magnetic field thatinduces a current in the inductor loop for energizing the LEDs.
 12. Thesystem of claim 1 wherein the light-generating devices comprise lightemitting diodes (LEDs) coupled to metal pads, wherein the energizingsystem applies a voltage to the metal pads for energizing the LEDs. 13.The system of claim 1 wherein the authentication tool is substantiallytransparent so markings over which the authentication tool is affixedremain visible.
 14. The system of claim 1 wherein the processing systemdetermines the presence of one or more light-generating devices in eachcell of a cell pattern applied to the authentication tool and generatesthe first code corresponding to locations of the light-generatingdevices in the cells.
 15. The system of claim 1 further comprising aprinted second code that is also detected by the detector and associatedwith the first code.
 16. The system of claim 15 where the second code isprinted on the authentication tool.
 17. The system of claim 15 where thesecond code is printed on an article to be authenticated by theauthentication tool.
 18. The system of claim 1 wherein thelight-generating devices are printed in a pattern that conveys anorientation of the authentication tool.
 19. The system of claim 1wherein the authentication tool is affixed over a surface, wherein theauthentication tool cannot be removed from the surface without affectingthe pattern of the illuminated LEDs.
 20. An authentication systemcomprising: an energizing system for illuminating randomly printedlight-generating devices on a substrate, wherein the light-generatingdevices comprise light emitting diodes (LEDs), the randomly printedlight-generating devices on the substrate being an authentication tool;an optical detector configured for detecting a pattern of thelight-generating devices in the authentication tool after thelight-generating devices have been illuminated; a processing systemcoupled to the detector and configured to generate a first codecorresponding to the pattern of the light-generating devices; acommunication system coupled to transmit the first code to a databasestoring pre-stored codes; and an interface system configured to conveythat the first code matched one of the pre-stored codes, signifying thatthe authentication tool is authentic; wherein the optical detector isconfigured to detect the pattern of the light-generating devices withina first area of the authentication tool, wherein the randomly printedlight-generating devices are excluded from a predetermined exclusionzone in the first area, wherein the exclusion zone in the authenticationtool forms a first pattern that has been previously stored in thedatabase, wherein the first code conveys a detected first pattern in theauthentication tool, wherein the communication system transmits thefirst code to the database for comparing the detected first pattern tothe first pattern stored in the database, and wherein the interfacesystem is configured to convey that the detected first pattern matchedthe first pattern stored in the database to verify that theauthentication tool is authentic.
 21. The system of claim 20 wherein theexclusion zone, forming the first pattern, in the authentication tool isselected from a set of exclusion zones when forming the authenticationtool.
 22. The system of claim 21 wherein the set of exclusion zones areapplied to other authentication tools, and wherein when all of theexclusion zones in the set of exclusion zones are superimposed over eachother there will be no overlap of exclusion zones and no gaps betweenexclusions zone.
 23. A method for authenticating an authentication tool,the authentication tool comprising printed light-generating devicesrandomly arranged on a substrate to form a pattern, the light-generatingdevices comprising light emitting diodes (LEDs), the method comprising:illuminating the randomly printed light-generating devices using a firstenergizing system to cause a current to flow through the LEDs; detectinga pattern of the light-generating devices in the authentication tool,using a first optical detector, after the light-generating devices havebeen illuminated; generating a first code corresponding to the patternof the light-generating devices; comparing the first code to pre-storedcodes in a database, the pre-stored codes corresponding to valid codes;and determining that the authentication tool is authentic if the firstcode matched one of the pre-stored codes; wherein the step of detectingcomprises detecting the pattern of the light-generating devices within afirst area of the authentication tool, wherein the randomly printedlight-generating devices are excluded from a predetermined exclusionzone in the first area, wherein the exclusion zone in the authenticationtool forms a first pattern that has been previously stored in thedatabase, wherein the first code identifies a detected first pattern inthe authentication tool, wherein the step of comparing comprisescomparing the first code to the pre-stored codes in the database todetermine whether the detected first pattern matches the first patternstored in the database, and wherein the step of determining comprisesdetermining that the authentication tool is authentic if the detectedfirst pattern matched the first pattern stored in the database.
 24. Themethod of claim 23 wherein the exclusion zone, forming the firstpattern, in the authentication tool is selected from a set of possibleexclusion zones when forming the authentication tool so that the firstpattern is unique to the authentication tool.
 25. A method forauthenticating an article comprising: providing a pattern of detectabledots on an authentication tool, wherein the authentication tool isassociated with an article to be authenticated, and wherein the dots areprevented from being located in a predetermined pattern of exclusioncells on the authentication tool; illuminating the dots using a firstenergizing system; detecting the pattern of exclusion cells in theauthentication tool, using a first optical detector, after the dots havebeen illuminated; comparing the detected pattern of exclusion cells to avalid pattern of exclusion cells previously stored in a database; anddetermining that the authentication tool is authentic if the detectedpattern of exclusion cells matched the valid pattern of cells.
 26. Themethod of claim 25 wherein the pattern of exclusion cells on theauthentication tool is selected from a set of exclusion cell patternswhen forming the authentication tool.
 27. The method of claim 26 whereinthe patterns of exclusion cells in the set of exclusion cell patternsare applied to other authentication tools, and wherein when all of theexclusion cell patterns in the set of exclusion cell patterns aresuperimposed over each other there will be no overlap and no gaps. 28.The method of claim 25 wherein the dots comprise light emitting diodes(LEDs), and the first energizing system causes a current to flow throughthe LEDs.
 29. The method of claim 25 wherein the dots comprise awavelength-conversion material, and the first energizing system applieselectromagnetic radiation to the wavelength-conversion material.
 30. Themethod of claim 25 wherein the dots comprise printednon-light-generating particles, and the first energizing system is alight source.